Subgap states in disordered superconductors

Abstract

We revise the problem of the density of states in disordered superconductors. Randomness of local sample characteristics translates to the quenched spatial inhomogeneity of the spectral gap, smearing the BCS coherence peak. We show that various microscopic models of potential and magnetic disorder can be reduced to a universal phenomenological random order parameter model, whereas the details of the microscopic description are encoded in the correlation function of the order parameter fluctuations. The resulting form of the density of states is generally described by two parameters: the width Gamma measuring the broadening of the BCS peak, and the energy scale Gamma_{tail} which controls the exponential decay of the density of the subgap states. We refine the existing instanton approaches for determination of Gamma_{tail} and show that they appear as limiting cases of a unified theory of optimal fluctuations in a nonlinear system. Application to various types of disorder is discussed.

Contribution to the JETP issue dedicated to the 80th anniversary of Prof. Anatoly I. Larkin (12 pages, 2 figures); minor changes, identical to the published version

References in corpus (3)

• Universal Broadening of the Bardeen-Cooper-Schrieffer Coherence Peak of Disordered Superconducting Films
• Mesoscopic fluctuations of the supercurrent in diffusive Josephson junctions
• Effective spin-flip scattering in diffusive superconducting proximity systems with magnetic disorder

Cited by in corpus (17)

• Quantum breakdown of superconductivity in low-dimensional materials
• Field-dependent nonlinear surface resistance and its optimization by surface nano-structuring in superconductors
• How many quasiparticles can be in a superconductor?
• Density of states in a two-dimensional chiral metal with vacancies
• On the application of Mattis-Bardeen theory in strongly disordered superconductors
• Tuning microwave losses in superconducting resonators
• Multifractally-enhanced superconductivity in thin films
• Unconventional superconductivity in low density electron systems and conventional superconductivity in hydrogen metallic alloys under pressure
• Subgap states in disordered superconductors with strong magnetic impurities
• Tuning vortex fluctuations and the resistive transition in superconducting films with a thin overlayer
• Superconductivity in La${}_2$Ni${}_2$In
• Droplets of the order parameter in a low density attracting electron system in the presence of a strong random potential
• Inhomogeneous magnetic multiband superconductors
• Magnetic disorder in superconductors: Enhancement by mesoscopic fluctuations
• Excess quasiparticles and their dynamics in the presence of subgap states
• Recombination of localized quasiparticles in disordered superconductors
• Surface density of states in superconductors with inhomogeneous pairing constant: Analytical results